Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:
RAT radio access technology
HCS hierarchical cell structure
RRC radio resource control
DRX discontinuous reception
LTE long term evolution
eNodeB evolved Node B (base station in the evolved UTRAN)
UE user equipment
EPC evolved packet core network
E-UTRAN evolved UTRAN
SAE system architecture evolution
UTRAN UMTS terrestrial radio access network (3GPP TS25.401)
GERAN GSM EDGE radio access network
GSM global system for mobile communication
EDGE enhanced data rates for GSM evolution
At present many network operators employ heterogeneous networks. This means that these networks are composed of different radio technologies (different RATs). For example, it is quite common to find a network operator providing both GERAN and UTRAN in the same geographical area. In the future one can expect to find GERAN, UTRAN and EUTRAN networks all under the control of a single network operator.
A terminal (e.g., also referred to herein as a UE, such as a cellular phone) operating in a heterogeneous network should be able to move smoothly and seamlessly between different RATs. For this reason, the access technologies include interworking capabilities to interact with other access technologies.
As more access technologies become available an operator may wish to create different subscription levels so that specific subscriber types can be assigned to specific collections of access technologies. However, this type of operation implies the existence of some guidance for terminals allocated to specific access technologies to move across these technologies. At present, there are no priority instructions given from the operator to terminal about which radio access technology should be a preferred one as compared to radio access technology.
In the case of GERAN-UTRAN interworking there is no explicit indication about which is the preferred system for the terminal to camp on. However, this is handled implicitly by setting up a cell reselection configuration in such a manner that it forces a terminal UE with GERAN and UTRAN capabilities to camp on the UTRAN network whenever possible. Alternatively HCS cell reselection criteria may be used for allowing some prioritization, especially from UTRAN to GERAN. However, the HCS cell reselection scheme has not been widely deployed due at least to a perceived problem of excessive parameterization. Additionally, not all terminals support HCS cell reselection.
Further, currently used simple methods for cell reselection priorities are not efficient if more than two RATs are available to the terminal, e.g., the terminal is allowed access to GERAN, UTRAN and EUTRAN networks.
In a dedicated mode the network may assign some prioritization, however this procedure is slow and increases the signaling load, as the network needs to signal the terminal every time an attempt is made to access another, higher priority access technology.
In general, cell reselection criteria for UTRA is defined in 3GPP TS 25.304, V7.1.0 (2006-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode (Release 7), and cell reselection criteria for GERAN is defined in 3GPP TS 45.008, V7.6.0 (2006-11), 3rd Generation Partnership Project; Technical Specification Group GSM/EDGE; Radio Access Network; Radio subsystem link control (Release 7.
Reference can also be made to commonly owned U.S. Pat. No. 6,751,460 B2, Methods and Apparatus for Performing Cell Reselection for Supporting Efficiently Hierarchical Cell Structures, Sari Korpela and Kaj Jansen.
Also of interest is commonly owned U.S. Pat. No. 6,978,142 B2, Cell Prioritizing in a Cellular Radio System, Matti Jokimies; commonly owned US Patent Publication No.: US 2006/0234705 A1, Method, Apparatus and Computer Program Providing for Rapid Network Selection in a Multimode Device, Paul Oommen; and commonly owned US Patent Publication No.: US 2006/0282554 A1, Method, Apparatus and Computer Program Providing Network-Associated System Priority List for Multimode System Selection, Jack Yuefeng Jiang, Paul Oommen, Yi Cheng and Liangchi Hsu.